I figured this out on my own. But for those who want to put the fortnites infinity gauntlet on Heavy without hand problems just follow my instructions. I experimented a bit.

First spawn the player model Heavy not the HWM
then bake the bones. It's in utilities then bake procedural bones
Next spawn the mad titan arms DONT LOCK YET
open up the arms and right click on the left hand. Add scale and shrink the hand all the way (dont forget the fingers)
Then lock and zero onto the heavy. (The fingers WILL come back but don't panic. Just go to the left fingers and select them all and right click. Add a scale and shrink them all.)
Put the rig on the heavy
next get the gauntlet and do what the instructions say, lock only the left lower arm onto the heavy
Zero the gauntlet on to Heavy
Last and not least lock the heavys left hand to the gauntlet.

Now you got a Thanos heavy with the Infinity war Gauntlet.
Just so you know I tried to see if I can get the fingers to work. Causes the cameras to freeze and the fingers dont move. You'll have to alternate back and forth with models to animate the fingers. But they still work.